1. Technical Field
The present invention relates to a liquid surface sensor and a liquid surface detection method.
2. Related Art
In the related art, a liquid surface sensor that detects a liquid surface of a liquid stored in a tank has been known (for example, see JP-A-2012-122784).
The liquid surface sensor described in JP-A-2012-122784 is provided with a buzzer on a sidewall surface within the tank and causes the buzzer to output a buzzer sound having a predetermined frequency. The liquid surface sensor detects the amount of liquid within the tank based on a change in sound pressure of sound produced from an entrance of the tank, which is determined by a Helmholtz resonant frequency changed based on a volume of a gas within the tank and a frequency of the buzzer sound within a range in which the Helmholtz resonant frequency is changed.
Incidentally, as described in JP-A-2012-122784, in the sensor that detects the liquid surface using the Helmholtz resonant frequency, acoustic matching between a resonant element (for example, buzzer) and a resonance target (for example, air within the tank) is bad, and thus, it is difficult to improve measurement precision of the liquid surface within the tank.
In the liquid surface sensor using the Helmholtz resonant frequency, since it is necessary to provide the buzzer on a side surface within the tank and it is necessary to form a sufficient space for storing the air as the resonance target, it is necessary to form a large measurement space, and thus, a measurement environment is restricted like a case where it is difficult to measure a narrow space.